Penems and carbapenems are antibacterials which are useful in animal and human therapy. These antibacterials are active against a broad range of pathogens, including gram positive bacteria such as S. aureas, Strep. pyogenes and B. subtilis and gram-negative bacteria such as E. coli, Pseudomonas, Proteus organii, Serratia and Klebsiella.
Numerous methods for preparing such antibacterials have been disclosed in U.S. Pat. Nos. 4,675,317; 4,663,451; 4,623,643; 4,614,614; 4,584,133; 4,530,793; 4,517,724; 4,504,485; 4,378,314 and recently in the article by S. Hanessian et al. JACS, 1985, 107, page 1438. This reference discloses a multi-step process for preparing penems, including converting L-threonine into an epoxy acid, then to the epoxamide, followed by treatment of the epoxamide with potassium carbonate in dimethylformamide which results in ring closure to give the azetidinone. It would be highly desirable to utilize intermediates which require fewer reaction steps than for those disclosed in the Hanessian et al. article, in order to simplify the preparation of penem and carbapenem antibacterials. It would also be desirable to utilize an intermediate which allows an easy and convenient insertion of blocking groups to prepae the penem and carbapenem antibacterials. It would also be desirable to provide a process for making such selected intermediates in good yields and which allows selective insertion of a wide variety of blocking groups at the nitrogen atom.